Moths Inspire Anti-Glare Coatings That Grab Light and Don’t Let Go
Stare into your partner’s eyes, and you might see love, admiration, resentment, or a heady combination of all three. Stare into a moth’s eyes, and you’ll see … well, nothing, probably. Not because moths are cruel, heartless creatures, but because moth eyes have evolved to reflect as little light as possible, and they end up looking a lot like inky voids.
It’s a self-defense mechanism. Humans use their eyes to communicate as well as see, but moths need to flit unnoticed past their predators while maximizing the light that hits their own eyes to see where they’re flying. So they use a nanostructure on the surface of their eyes called, delightfully, a corneal nipple array. Essentially, moth eyes are covered in tiny cones, a layer that sort of resembles a stand of Douglas firs.
Those little cones cluster together so closely—with distances narrower than the wavelength of light—that incoming light can’t differentiate between air and the material it’s about to hit, and never ends up reflecting back out. “You trick the light, basically,” say Chih-hung Chang, a chemical engineer at Oregon State University whose lab is developing anti-reflective coatings. The result: Light just falls into the material as if it were a black hole, or, you know, Hotblack Desiato’s extravagant stuntship in Douglas Adams’ Hitchhiker series.
Humans don’t have to worry about getting spotted by bats and snapped up for dinner, but materials that grab onto light and don’t let go can come in handy. So nanomaterials scientists have made like moths and developed coatings with these tiny light-trapping cones. Glass reflects about 4 percent of the light that hits it, Chang says, while science has managed to get these coatings to reflect less than half a percent back. Slapped on transparent materials like glasses or iPhone screens, they cut down on glare. Apply a moth-eye coating to a silicon wafer, and it’ll look like a small square hole to space just opened up in front of you.
Which is why scientists are now especially keen on putting these high-tech coatings on solar cells. The more light solar panels can hold on to, the more fodder they have to generate electricity, and ultimately, the more cost-effective and efficient the photovoltaics are. Those nanostructures are grabby that way, all take and no give. Maybe you’re better off not looking into that moth’s eyes.